This invention relates to stratified charge engines and more particularly to a combustion chamber for swirl flow two valve spark ignition direct injection (SIDI) engines.
Spark ignition direct injection (SIDI) combustion systems for internal combustion engines have been proposed to improve fuel economy when compared with more typical port fuel-injected combustion systems. The spark ignition direct injection engine is provided with a high pressure fuel injection system that sprays fuel directly into the engine combustion chamber, which is formed at least partially in the piston. The fuel is directed or transported to a specific region within the combustion chamber. This creates a stratified charge in the combustion chamber resulting in fuel economy benefits, since the throttling requirements are less restrictive and the fuel combustion characteristics are improved. Development of such engines has been primarily directed to engines having dual intake valves adapted for creating cylinder air swirl for stratified charge operation in a lower power range and for maximizing intake air flow for increased power in a higher power range. Conventional high pressure fuel injectors may be used in such engines.
U.S. patent application Ser. No. 09/930,707 filed Aug. 13, 2001 and assigned to the assignee of the present invention, discloses an improved combustion chamber for a SIDI engine having four valves per cylinder. The piston includes an oblong or oval shaped bowl, forming 50% to 70% of the total combustion chamber volume at piston top center, into which a fuel spray is injected during the piston compression stroke. Development is desired of a practical combustion chamber for a stratified charge engine having only two valves per cylinder, including a single intake valve and a single exhaust valve.
The present invention provides a combustion chamber and piston bowl design for a spark ignition direct injection (SIDI) engine having two valves per cylinder.
The combustion chamber is defined by a cylinder having a closed end including a wedge shaped combustion chamber recess. A fuel injector extends through the closed end near a shallow side of the wedge recess and a spark plug extends through the closed end at a deeper part of the wedge recess opposite from the injector. A single pair of laterally spaced intake and exhaust valves control intake and exhaust ports opening into the wedge recess generally between the injector and the spark plug.
The combustion chamber is further defined by a piston in the cylinder, the piston having an outer diameter and a head end facing the end of the cylinder. The head end includes a raised pedestal with a shallow upwardly angled face ending at a raised ridge and enclosing a shallow bowl in the head end. The bowl is generally oval with a major dimension generally aligned with a cylinder centerline through the valves.
The intake port is configured to generate a swirling flow of intake air in the cylinder during the piston intake stroke. The injector is aligned to inject a spray of fuel into the piston bowl during the piston compression stroke so that the fuel and air form in the bowl a swirling flow of stratified locally rich mixture that is compressed and directed by the piston ridge to the spark plug for ignition of the stratified air fuel charge near the end of the compression stroke. Preferably the fuel spray is angled to one side toward the direction of air swirl in the bowl as well as downward toward the bowl.
These design features are utilized to create a cloud of flammable fuel-air mixture and move it toward the spark plug at an ignition timing that results in high engine efficiency. Efficiency is obtained by operating the engine unthrottled at part loads, where load control is obtained by overall lean operation (approximately 45/1 air fuel ratio) and high dilution (approximately 35%) with residuals and exhaust gas recirculation.